1. Field of the Invention
The subject invention relates generally to computer systems, and more particularly to a method of resetting subsystems connected to a system master computer in response to error conditions, using address dependent RC discharge circuitry.
2. Description of Related Art
Most computer systems and subsystems rely on a power up reset, typically timed by an RC network, to begin an orderly execution of their primary tasks with well-known initial conditions. When an error condition (fault) occurs from which the system has no way of recovering, the faulty system or its faulty subsystem will completely stop execution of its primary task, or worse, begin to behave in an unpredictable manner.
There are two methods in which most systems handle such faults. According to one method, task execution is halted and an error message identifying the faulty subsystem is transmitted to the system operator. The system operator may respond by powering down the entire system and then powering it up again to allow the system master and its subsystems to restart in an orderly manner. Alternatively, the system operator may respond by manually pushing a mechanical switch located on the faulty subsystem, which discharges an RC-timing network, thus simulating a power up reset on the faulty subsystem. After resetting the faulty subsystem, the operator commands the system master to continue task execution. In the second method, the system master detects the fault condition, for example, through an error message or time-out, and communicates a reset command to the faulty subsystem. The faulty subsystem then executes the command and resets itself.
There are problems with the above recovery processes. In the first method, intervention by a human operator is needed, making the system less than fully automatic and slow to recover from a fault condition. Also, powering down the entire system forces all the subsystems to reset, which unnecessarily interrupts subsystems which are operating properly. In the second method, where the system master automatically communicates a recovery command to the faulty subsystem, the faulty subsystem may be unable to interpret the command because of the nature of the subsystem fault. Additionally, in some cases, the second method is not practical because some subsystem microprocessors cannot assert a reset signal to reset themselves and supporting circuitry to a known initial condition.